<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
    <script>
        let year=Number(prompt(''))
        let month=Number(prompt(''))
        switch(month){
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:
                alert('这个月有31天')
                break
            case 1:
            case 4:
            case 6:
            case 9:
            case 11:
                alert('这个月有30天')
                break
            default:
            if (year%400===0||(year%4===0 &&year%100!==0)){
            alert('这个月有29天')
        }else {
            alert('这个月有28天')
            break

        }

        }
        
    </script>
</body>
</html>